About building insulation materials, Part 1
When it comes to energy conservation, one of the first suggested upgrades for your new or existing home is building envelope insulation. It’s not the easiest of upgrades, but it is certainly one of the most efficient and performance-enhancing.
Building insulation materials form the thermal bridge between the inside and outside temperature heat transfer. There are many different materials to choose from, and far too many for this discussion. A few examples include the newest petroleum products, such as polyethylene foam, extruded and expanded polystyrene (EPS and XPS) to the more popular fiberglass batts, and cellulose wet spray. There are also the more natural cardboard, cotton, wool, straw and wood chip insulators.
Insulation is categorized by its material composition, natural or synthetic; its form, batts, blankets, loose-fill, spray foam and panels; its structural contribution (insulating concrete forms) and structured integrated panels (ISP); its functional mode (conductive, radiative, convective), its resistance to heat transfer; and its environmental impact.
The maximum thermal performance, or R-value, of insulation is dependent on its form and function; however, correct installation is key to absolute performance. Homeowners can install some types of insulation - notably blankets, batts and materials that can be poured in place, but other types require professional installation.
Below we will look at the most popular residential solutions.
Fiberglass, which consists of extremely fine glass fibers, is the most common residential insulating material, and is usually applied as batts, blankets and loose-fill; it is also available as rigid boards and duct insulation. Batts and rolls are available in widths suited to standard spacing of wall studs, attic trusses or rafters, and floor joists.
Manufacturers often attach a facing (such as Kraft paper, Foil-Kraft paper or vinyl) to act as an air barrier, radiant barrier, and/or vapor barrier and some even provide flame resistance. Batts with a special flame-resistant facing are available in various widths for basement walls and other places where the insulation will be left exposed. A facing also protects the insulation’s surface, holds the insulation together, and facilitates fastening to building components. Loose-fill insulation must be applied using an insulation-blowing machine in either open-blown applications (such as attic spaces) or closed-cavity applications (such as those found inside walls or covered attic floors).
As stated, installation is critical as gaps can become sites of air infiltration or condensation, both of which reduce the effectiveness of the insulation and encourage mold and insect infestation. Cutting to accommodate electrical boxes and other obstructions also allows air a free path to cross through the wall cavity. Compressing the material also reduces its effectiveness. By the same token, careful weatherization and installation of vapor barriers ensure that the batts perform well.
Standard fiberglass blankets and batts have a thermal resistance or R-value between R-2.9 and R-3.8 per inch of thickness. This determines a 6-inch thickness to meet a 2012 wall building code of R-19.
Green building practices shun fiberglass insulation, as fiberglass is energy-intensive in manufacture, and health and safety issues include potential cancer risk from exposure to glass fibers, formaldehyde off-gassing from the backing resin, use of petrochemicals in the resin, and the environmental health aspects of the production process. However, fiberglass batts are very cost competitive at between 60 cents and $1.20 per square foot installed.
Cellulose insulation is popular in energy-efficient new and existing homes as it is environmentally preferable and safe. It has a high recycled content and less risk to the installer than fiberglass, and it’s not made from petrochemicals or chemicals with a high toxicity and no formaldehyde-based binders. It is made from recycled paper products, primarily newsprint, and it is denser and more resistant to air flow than fiberglass. The shredded paper is mixed with one of several fire retarders and insect repellants, most commonly borate acid and borax; loose fill insulation fills the wall cavity better than batts.
Cellulose can also be sprayed in place, usually with water-based adhesives. Spray application provides even better protection against air infiltration and makes the cellulose more resistant to settling; it also improves wall rigidity. Wet-spray is best for new construction, as the wall must be allowed to dry completely before sealing with drywall. Moisture is always a concern for homes, and the wet-spray application of cellulose may not be a good choice in particularly wet climates unless the insulation can be verified to be dry before drywall is added, as mold has been seen as a potential concern.
The insulating value of cellulose is comparable to that of fiberglass batts (R3.2 to R3.8); however, because cellulose is more resistant to airflow than fiberglass, it performs much better. Cellulose insulation is also inexpensive. The cost to install R-19 or R-21 of dense-packed cellulose in a 2-by-6-foot wall is 81 cents to $1.80 per square foot, and loose-fill installed to R-38 is between 42 cents and 99 cents per square foot.
Proponents of green building appreciate its high recycled content and low embodied energy. One disadvantage of cellulose is that it doesn’t respond well to moisture. Because cellulose is able to absorb and hold a lot of water, roof or plumbing leaks may go unnoticed longer than with other insulation materials and cause significant damage.
Next time, we will discuss spray foam insulation.
Contact Paul Scrivens www.greenhomeenergyadvisors.com